This invention relates to condition sensing cable devices useful in oceanographic work, and more particularly to an improved cable construction of the type comprising a plurality of hydrophones or other transducers spaced along a cable to form a line array.
Devices of the foregoing character are at times deployed by streaming horizontally from a moving tow vessel, and at times are suspended vertically in the water. In any event, size, weight, and particularly flexibility of the cable type of line array device are important factors affecting ability to handle, deploy, recover, and store the device using available deck machinery and without the requirement of additional special handling equipment. Another portant consideration is the capability of the cable array, and particularly the wire conductors and transducer elements, to withstand the bending, flexing, and jerking forces imposed by either being towed from a vessel or suspended from a buoy subjected to surface wave action.
A variety of hydrophone cable or line array devices have been used or proposed in the past having a plurality of discrete sensors spaced therealong. Examples include those described in U.S. Pat. Nos. 3,518,677 to E. F. Florian, and 3,531,760 to W. A. Whitfill, Jr. All of the foregoing are relatively complex, expensive, and as a very important consideration are not readily made up or changeable on site as to transducer number and location along the cable.
Among recent materials advances that have contributed to lighter, stronger and more flexible electroacoustic cable devices is that of aramid fibers which are characterized by their strength, high resistance to stretch, their lightness in weight, and their flexibility. U.S. Pat. No. 3,939,464 to R. C. Swenson, the inventor herein, discloses a cable sensor mount in combination with a cable comprising aramid fibers formed in four sections, each separately covered, and a plurality of groups of conductors lying in the interistices between the fiber sections, the cable sections and conductor groups all being held together and protected by a braided cover of nylon, or the like. The sensor mount comprises a cylindrical, open, sensor housing framework or cage, preferably of stainless steel, and a pair of relatively short tapered flexible polyurethane cones or fairings fixed to opposite ends of the cage. The mount is inserted between or among the fiber sections that have been spread apart and lie in four parallel grooves defined in the cage and fairings. The cage structure comprises split ring ends connected by grooved strongbacks and fastened to additional end rings by screws. The end rings comprise formed extensions of the strongback grooves and are aligned with the grooves in the flexible fairings. Further improvements in cable arrays and sensor mount constructions are described in the copending patent application of Richard C. Swenson, Ser. No. 955,542, filed Oct. 27, 1978, and assigned to the assignee hereof now U.S. Pat. No. 4,241,427. The cable array described therein comprises pairs of conductor containing, hollow braided strands plaited into a hollow braid in which transducer mounts are enmeshed and gripped. The mounts comprise a rigid plastic tubular housing in which a rubber jacketed transducer is resiliently suspended by elastomeric projections. Resiliently flexible, hollow, tapered, rubber fairings extend from each end of the housing and are slit to admit wires pulled from a cable strand. The fairings are long relative to the housing diameter and are retained assembled with the housing by cooperating ribs and grooves. The cable further comprises an outer, tightly braided cover which can be cut away to add or remove sensor mounts and then repaired by braiding or applying a laced jacket to replace the area of removed cover. That array cable, like its predecessors, comprises many wire conductors, i.e., a pair for each transducer station. The wire conductors in the foregoing and other cable arrays have been embedded within strands or in the body of a cable so as to be gripped, supported, or held in place substantially throughout their lengths and have had to be formed with a helix in order to minimize breaking due to stretch, bending, or jerking of the cable in use.
While those cable and sensor mount constructions have provided notable improvements over the earlier mentioned prior art with respect especially to versatility and flexibility, the requirements of many conductor wires in the cable and an outer, tightly woven or braided cover layer render the cable arrays heavier, more prone to failure of conductors, more expensive, and more difficult to insert or remove sensor stations than is desired. In addition, the requirement of providing a helix in the conductors introduces additional expense and manufacturing steps.
Other shortcomings in prior art cable arrays using synthetic fiber protective covers have been experienced in the terminal or end fittings in that synthetic fibers such as nylon, aramid, and the like, are difficult to provide with reliable end fittings for supporting the array and allowing for electrical connections to the numerous conductors.